CVE-2023-27076: Tenda G103 Firmware RCE Vulnerability

CVE-2023-27076 Overview

CVE-2023-27076 is a command injection vulnerability discovered in the Tenda G103 router firmware version 1.0.0.5. This security flaw allows remote attackers to execute arbitrary code on the affected device by exploiting improper input validation in the language parameter. As a network-accessible vulnerability requiring no authentication or user interaction, this flaw poses a significant risk to affected devices and the networks they serve.

Critical Impact

Remote attackers can achieve full system compromise on Tenda G103 routers by injecting malicious commands through the language parameter, potentially leading to complete device takeover, network pivoting, and persistent backdoor installation.

Affected Products

• Tenda G103 Firmware version 1.0.0.5
• Tenda G103 Hardware devices running vulnerable firmware

Discovery Timeline

• April 10, 2023 - CVE-2023-27076 published to NVD
• May 5, 2025 - Last updated in NVD database

Technical Details for CVE-2023-27076

Vulnerability Analysis

This command injection vulnerability (CWE-78: Improper Neutralization of Special Elements used in an OS Command) exists due to insufficient input sanitization in the Tenda G103 router's web management interface. The firmware fails to properly validate and sanitize user-supplied input passed through the language parameter before incorporating it into system commands executed by the underlying operating system.

Command injection vulnerabilities in embedded devices like routers are particularly dangerous because these devices typically operate with elevated privileges and serve as critical network infrastructure components. Successful exploitation grants attackers the ability to execute arbitrary commands with the same privileges as the web server process, which on embedded Linux systems often runs as root.

The network-accessible nature of this vulnerability, combined with no authentication requirements and no user interaction needed, makes it highly exploitable. Attackers can target vulnerable devices directly over the network without requiring any credentials or social engineering.

Root Cause

The root cause of CVE-2023-27076 lies in the firmware's failure to implement proper input validation and sanitization for the language parameter. When processing requests that include this parameter, the firmware directly incorporates the user-supplied value into a system command without escaping shell metacharacters or validating the input against an allowlist of expected values.

This implementation error allows attackers to break out of the intended command context by injecting shell metacharacters such as semicolons, pipes, or command substitution operators, followed by arbitrary commands that the system will execute.

Attack Vector

The attack is network-based and can be executed remotely against any Tenda G103 router with firmware version 1.0.0.5 that is accessible over the network. Attackers craft malicious HTTP requests to the router's web management interface, embedding shell commands within the language parameter.

The exploitation process typically involves:

1. Identifying a vulnerable Tenda G103 router through network scanning or reconnaissance
2. Crafting a malicious HTTP request with command injection payload in the language parameter
3. Sending the request to the target device's web interface
4. The injected commands execute on the underlying system with elevated privileges

Technical details and proof-of-concept information are available in the GitHub PoC Repository maintained by security researchers.

Detection Methods for CVE-2023-27076

Indicators of Compromise

• Unexpected outbound network connections from the router to unfamiliar IP addresses
• Unusual processes or services running on the device that are not part of standard firmware
• Modified configuration files or new user accounts on the router
• Unexplained DNS query patterns or traffic routing changes
• Evidence of shell metacharacters (;, |, $(), backticks) in web server access logs targeting the language parameter

Detection Strategies

• Monitor HTTP request logs for suspicious patterns in the language parameter containing shell metacharacters or command sequences
• Implement network-based intrusion detection rules to identify command injection attempts targeting Tenda router endpoints
• Deploy network segmentation monitoring to detect unusual traffic originating from router management interfaces
• Utilize SentinelOne Singularity platform for network device anomaly detection and threat hunting capabilities

Monitoring Recommendations

• Enable verbose logging on network infrastructure devices and aggregate logs to a central SIEM
• Implement network traffic analysis to detect anomalous behavior from IoT and network devices
• Establish baseline behavior for router management interface access and alert on deviations
• Monitor for reconnaissance activities targeting router web interfaces across your network

How to Mitigate CVE-2023-27076

Immediate Actions Required

• Identify all Tenda G103 devices running firmware version 1.0.0.5 in your environment
• Restrict network access to the router's web management interface to trusted administrative networks only
• Implement network-level access controls to prevent unauthorized access to router management ports
• Consider replacing vulnerable devices if no firmware update is available from the vendor

Patch Information

At the time of this publication, no official security patch information from Tenda has been documented in the CVE record. Organizations should monitor Tenda's official support channels for firmware updates addressing this vulnerability. Contact the vendor directly to inquire about remediation options for affected devices.

Workarounds

• Disable remote web management access to the router if not required for operations
• Place vulnerable devices behind a firewall or VPN to restrict management interface access
• Implement Web Application Firewall (WAF) rules to filter requests containing shell metacharacters in the language parameter
• Consider network isolation for vulnerable devices to limit potential lateral movement in case of compromise

# Example: Restrict management interface access using iptables on upstream firewall
# Allow only specific trusted admin IP to access router management
iptables -A FORWARD -d <router_ip> -p tcp --dport 80 -s <trusted_admin_ip> -j ACCEPT
iptables -A FORWARD -d <router_ip> -p tcp --dport 80 -j DROP
iptables -A FORWARD -d <router_ip> -p tcp --dport 443 -s <trusted_admin_ip> -j ACCEPT
iptables -A FORWARD -d <router_ip> -p tcp --dport 443 -j DROP